The human large bowel (colon), and to a lesser extent the small bowel, contain large concentrations of various enteric bacteria. They may range in concentration from between 10.sup.2 to 10.sup.7 per cubic centimeter in the small bowel and up to 10.sup.14 per cubic centimeter in the large bowel. When the bacteria are non-pathogenic, then the bowel produces no symptoms in the body.
On the other hand when the normal bowel flora is invaded or joined by pathogenic bacterial strains which may colonise the bowel and remain there long-term, chronic illness can result.
The local effects of abnormal bowel flora may include abdominal cramps caused by colonic or small bowel contraction, distension caused by either fluid or gas accumulation, diarrhoea caused by inadequate fluid absorption or excessive secretion, or constipation by abnormal motility patterns and excessive absorption of water. Severe local effects of abnormal bowel flora can include microscopic or collagenous colitis, ulcerative colitis, Crohn's disease and diverticulosis. Some of these effects are caused by local toxins, others by invasion of bacteria into the bowel lining and in others, the mechanisms are unknown.
When obvious, visible or microscopic colitis is present, it is known that beneficial clinical effects can be obtained from well known anti-bacterial drugs derived from salicylic acid, such as sulfasalazine (prepared by coupling 2-sulfanilamidopyridine with salicylic acid), 4-aminosalicylic acid, 5-aminosalicylic acid, and benzalazine.
When there are no visible abnormalities detectable in the colon and when stool tests, histology and blood tests are negative, yet patients still complain of symptoms referrable to the colon, a diagnosis of IBS will often be made. Some 10-25% of the Western population suffer with this disorder which has also been termed spastic or irritable colon, unstable colon, colonic neurosis, spastic colitis or mucus colitis. In the classic case, there is a triad of .symptoms including lower abdominal pain relieved by defecation, alternating constipation and diarrhoea and the passage of small calibre stools. Abdominal distension, flatulence or wind are also frequently present, as is passage of mucus as well as the sensation of incomplete evacuation. All these symptoms are present in the absence of demonstrable organic disease.
The pathogenesis of IBS has hitherto been unknown. Emotional disturbance, fibre deficiency, purgative abuse and food intolerance have all been implicated but not proven nor well demonstrated. Evidence for infection or autoimmunity is lacking. Conventional treatments for IBS have been unsatisfactory, as instanced by the very number of therapies that have, from time to time, been recommended or trialled. These have ranged from psychotherapy and dietary regimes to medication by antispasmodic agents, anticholinergic agents, barbiturates, antidepressants, bulking agents, dopamine antagonists, carminatives, opioids, and tranquillisers; all without signal success. There is no evidence that cure is possible.
IBS is one of the most common of the gastrointestinal illnesses, and though not life-threatening, causes great distress to those severely afflicted and brings a feeling of frustration and helplessness to the physicians attempting to treat it.